The digital era that is now upon us has the potential to change the way everyone operates in the motion picture field. The traditional method for projecting motion picture film was relatively simple because there were not very many options available to be controlled. Basically, film has a certain appearance or “look” that can be altered by processing, lighting and laboratory methods. The digital age has brought to the motion picture industry the ability to capture a motion picture print image and structure it in the form of data. Once the data has been captured, it can be manipulated practically to any degree that is desired. However, the more variables one has to work with, the harder it is to maintain or reconstruct the original intent.
A very large amount of program material potentially useful for electronic conversion exists, or is captured, in the form of photographic film. The type of equipment capable of producing digital signals from such film material is usually called a telecine scanner, or telecine for short. However, a motion picture film that, when projected in a dark auditorium, appears to be of perfectly satisfactory quality, may prove disappointing when converted for electronic viewing by means of a telecine. For this reason, it is possible to apply very useful adjustments to the pictures electronically. These corrections are typically applied by a colorist working in a telecine lab, and the corrected electronic signals are written out to a digital intermediate, such as a hard drive or other type of digital memory. In the terminology of the industry, the colorist “grades” the scanned film to an optimum “look” for film or video output based on a CRT monitor. This requires a lot of guesswork on the part of the colorist when the data is committed to film.
Today colorists in a digital mastering or telecine lab are somewhat limited in the viewing environment available to them while adjusting the tone scale and color of a digital image originating from scanned motion picture film or other digital capture device in order to produce an acceptable digital master. Equipment such as waveform monitors and vectorscopes can monitor the vast adjustment capabilities resulting from telecine and/or secondary color correction yet the motion imagery is typically displayed during this color grading process using a video monitor with a color gamut that is smaller than the scanned film. Additionally, the current process for injecting a desired “look” (such as that of a release print film) while color grading, typically relies on 1-dimensional hardware look up tables (1D LUTs) implemented within these limited gamut video devices and the subjective creative control of a colorist. (The 1D aspect of a LUT means that one output value is looked up for each input value.)
In the prior art, a given “look” can be attained through various adjustments using “primary” or “secondary” color correctors, such as da Vinci™ color corrector offered by da Vinci Systems Inc., with or without a telecine machine. In the patent literature, U.S. Pat. No. 5,255,083 describes a digital color correction system and method for color correction in a film-to-video signal conversion system. U.S. Pat. Nos. 5,140,414; 5,374,954; 5,406,326; 5,457,491 and 5,687,011 (each issued to Mowry) represent a family of related post-production video technology that seeks to arrive at an aesthetically acceptable simulation of the appearance that images originated on different motion picture film stocks would embody after telecine “flying spot scanner” transfer to video from taped high definition video originated images. One component of this prior art technology deals with the conversion of the video-originated material through a LUT that is based on color temperature of the scene lighting, scene brightness and selected f-stop setting. The conversion values in the LUT are derived by filming color charts and grey scale charts, obtaining a digital representation of the film component responses of the charts from telecine transfer of the film to videotape, and then charting the telecine-derived component responses against video originated images of the same charts under identical lighting conditions. The final simulated video image is either recorded as a high definition signal, or converted to an NTSC signal and broadcast or displayed.
In the latter two of the aforementioned Mowry patents, the digitized video signal may be sent to a film recorder, which reproduces the component-modified images onto a selected, reversal film stock. The film is chemically processed with a film processor and then optically projected, or scanned to video, digital video, or other electronic media. If the film recording option is employed, these patents specify that it is important that the telecine-derived LUT used in the component modification involves response data which compensates for the inherent color response of the film stock on which the images are being digitally recorded.
These systems may be able to come perceptually close to achieving a given “look” through trial and error, but have a tendency to introduce noise or other artifacts into the imagery in the process and are time consuming. In addition, there are colors that cannot be easily attained using conventional 1D look up tables (1D LUTs) and 3×3 matrices that may result from non-linear channel interdependencies.
What is needed is a straightforward robust method for emulating known “looks” (e.g. release film print) in real time on motion imagery with an expanded color gamut as part of an overall system that is capable of providing otherwise unattainable colors, all the while complementing existing products that perform color correction on motion imagery.